Children, children. Let's not go crazy over this one: forget the double meanings, whatever they may be. First and foremost, it's got two fingers because it is part TWO. They will not use it for a part three, because the two fingers would not correlate. Obviously. Secondly, yes, they justified it in the film as the Ghostbusters SECOND time around.
As for any secondary double meanings - they were secondary. I'm sure there was heavy pressure studio wise to give the GB's a new style (jump-suits, technology, symbol) and the two fingers thing is a good indicator. That being said, it was a dumb decision. This kind of shit is indicative of when a studio makes a bad sequal and screws with what worked the first time. I'm sorry, but the two business just cheapens the look.
Nick